This invention relates to fiber-optic cable, and particularly to termini, connectors, alignment devices and optical systems and methods for terminating and connecting fiber-optic cable.
Providing suitable end termini and connectors for connecting two fiber-optic cables together long has been a demanding problem. The problem has been exacerbated by the prevalent use of single-mode fiber-optic light conductors of an extremely small diameter, such as 8 micrometers (0.008 millimeters). To align the cables accurately usually is a time-consuming and exacting process.
Standard commercial butt-joint type single-mode fiber-optic connectors suffer from numerous problems. First, they are relatively delicate, sensitive to dirt, difficult to clean, and easily damaged. The problems are even greater with multi-channel connectors which must function in a hostile environment.
In the past, various proposals have been made to improve such prior connectors. Included are proposals to use expanded-beam type connectors. Such connectors use different types of lenses to collimate and spread the beam of light emitted from the optical conductor. Then, an identical lens system is used to terminate another cable end to be coupled to the first cable, and the two termini are connected together. The second lens system re-focuses the beam on the second optical conductor so as to transmit the signal through the second cable.
The optical systems used in such prior expanded-beam connectors include spherical lenses, xe2x80x9cGRINxe2x80x9d lenses (graded index lenses) and molded aspheric lenses to expand and collimate the light beam.
The advantages of such expanded beam connectors includes minimizing the sensitivity to lateral misalignment and to the size of the gap between the ends of the optical conductors.
However, prior expanded beam connectors and techniques suffer from several problems. Such problems include relatively high optical losses and high cost. In fact, the cost has been considered to be prohibitive for many commercial applications. Furthermore, it is believed that the prior designs are relatively difficult or even impossible to be installed correctly in the field; that is, outside of a factory, laboratory, or other such facility.
Accordingly, it is an object of the present invention to provide a terminus, connector and alignment device and method which overcome or alleviate the foregoing problems.
More specifically, it is an object of the invention to provide an expanded-beam type terminus and connector and alignment device and method which overcome or reduce the problems experienced with prior expanded beam devices.
In particular, it is an object of the invention to provide a fiber-optic cable terminus and connector which has as many of the following favorable attributes as possible: low cost; low loss; low back-reflection; small size; ruggedness; insensitivity to dirt; ease of cleaning; capability of being installed in the field; high optical power throughput capability; suitability for use in hostile environments; and capable of being standardized.
It is also an object of the invention to provide such a device and method capable of operating with single mode optical conductors; with multi-channel cable; is relatively non-dichroic; and preserves polarization of the light being conducted.
It is another object of the invention to provide an integrated multiple-reflector optical device for expanding and collimating light beams and particularly fiber-optic cable light beams.
In accordance with the present invention, the foregoing objects are met by the provision of a fiber-optic cable terminus, connector and alignment device and method as follows.
A terminus having a first reflector for reflecting the beam received from one optical conductor is provided. A second reflector reflects the beams from the first reflector to form expanded and collimated light beams.
Preferably, the system of reflectors is like that in a Cassegrainian or Ritchey-Chretien reflecting telescope system. Such systems have been used for many years in the field of astronomy. Applicants have recognized that, even though the telescope systems usually are very large and expensive, the small devices used in this invention can be made relatively inexpensively. The use of reflectors or mirrors rather than lenses tends to minimize the effects of refraction which so often increases the difficulty in the optical design process for the usual prior art proposals for beam-expanding connectors.
The resulting optical system is very compact, relatively amenable to standardization and inexpensive to manufacture.
In accordance with another feature of the present invention, the problem of aligning light conductors in fiber-optic cables is substantially alleviated by providing a magnetically permeable element adjacent to the optical conductor, applying a magnetic field to the magnetically permeable member, and controlling the field to move and align the conductor. Movement in at least two orthogonal axes is preferred.
Preferably, proper alignment is tested by passing a signal through the cable and a second cable, and determining when the signal transmission is maximized.
The optical conductor is then fixed in position. Preferably, this is done by injecting a radiation-curable plastic material such as epoxy resin into the area surrounding the conductor end, and irradiating it to harden the epoxy when the alignment is correct. Specifically, an embodiment of the invention uses light-curable epoxy resin. Light is directed to the epoxy to perform the curing.
It also is preferred that the magnetic field source be one for developing a rotating magnetic field which rotates around the optical conductor end, with an electrical network being provided to control the field. This allows movement of the effective center of the magnetic field, and precise positioning of the conductor end.
It also is preferable that the magnetically permeable member be approximately toroidal or cylindrical, with a frustro-conical inlet to the central opening to guide the conducting fiber into the central opening during installation.
The invention also provides a compact integrated optical device for spreading and collimating light. A block of transparent material such as glass or plastic, is provided with surfaces shaped to form reflectors of the size, shape and position desired and then those surfaces are coated with a reflecting material such as metal. This can be done at a reasonable cost by vapor deposition, sputtering, etc.
The foregoing and other objects and advantages of the invention will be set forth in or apparent from the following description and drawings.